1. Field of the Invention
This invention relates to a picture image discriminating apparatus for discriminating a picture image of document beforehand whether it is a linear picture with a line working as a principal constituent or a tonal picture consisting of a continuous tone so as to obtain a satisfactory reproduction on a reproducing apparatus. More particularly, it relates to a picture image discriminating apparatus for discriminating a picture image of document according to an electrical picture signal which is obtained from a light signal corresponding to the picture image through scanning the document.
2. Description of the Prior Art
An improvement in reproducing technique has effected of late a reproduction meeting a picture quality of the document consisting only of a linear picture or a tonal picture. To say concretely, the linear picture or the tonal picture is discriminated visually, there is prepared an independent operating button to specify reproducing conditions for the linear picture or the tonal picture, and thus an operator will select the suitable operating button according to a result obtained through visual observation, thereby obtaining a reproduction. Therefore, an erroneous decision or operation may lead to a wasteful reproduction.
In the existing circumstances wherein a high-speed and efficient operation is required for reproduction, and a copying machine provided with an automatic document feeder (ADF) has come rapidly into wide use therefor, an operation for picture image discrimination which depends, as mentioned, on visual observation is not to cope with the object of high-speed and efficient operation and is practically impossible for application on the copying machine provided particularly with ADF.
On the other hand, in case a picture image data is compressed to transmission or store like facsimile or picture image data base, an information compression efficiency is not secured satisfactorily unless coding process is applied to each linear picture and tonal picture, thus requiring a picture image discriminating apparatus.
As one of picture image discriminating methods, there prevails hitherto a method (U.S. patent application Ser. No. 292,012 filed Aug. 11, 1981, now abandoned) which comprises scanning a document, forming a histogram according to a density distribution at each point of the document, and thus deciding a picture image from a pattern of the histogram, however, while it is effective chiefly to a linear picture information, an application to a tonal picture is difficult. Moreover, a process for discrimination is complicated.
Then, a method to use the histogram described hereinabove requires a central processing unit like microprocessor for arithmetic operation of a data statistics, conversion, etc. and decision and a memory such as ROM and RAM essential for operation of the above unit, thus involving high cost and complicatedness.